A SYSTEM FOR IDENTIFYING A SENSOR AND MEASURING FLOW IN A FLOW DUCT

Description

Field of the Invention

[0001] The present invention relates to a system or a method for measuring flow of fluid or gas, which system comprises a flow duct, which flow duct comprises at least two transducers, which transducers generate at least one beam of ultrasound in the flow duct.

Background of the Invention

[0002] A non-published Danish patent application PA 2012 70241 filed by the same applicant disclose a system or a method for measuring flow in a flow duct, comprising at least two ultra sound transducers. It is the object of this application to measure the flow of air in a duct by one or more transducers transmitting beams of ultra sound controlled by a microcontroller based electronic system. The object can be achieved if the microcontroller stores a vector of data samples for each direction of transmission, which vector comprises an appropriate number of N samples forming a frame, which microcontroller multiply each value of the frame which a complex number, which microcontroller based on the result calculates the flow in the duct. By the invention according to the present patent application an efficient flow measurement of air flowing in a duct can be achieved.

[0003] Other published patent applications such as WO 93/00569, WO 2010/122117 A1 and US 2013/0061687 A1 are identified as belonging to the prior art.

Object of the Invention

[0004] The object of the pending application is to place ultrasound transducers in a fixed position in a duct for flowing air where the electronic device for analysing signals from the transducers is placed in a handheld device. A further object of the pending patent application is to achieve automatic calibration and adjustment of the handheld device depending on the dimensions of the measuring duct.

Description of the Invention

[0005] The object can be achieved by a system as disclosed in the preamble to claim 1 and further modified by the transducers receiver circuit is placed in a handheld device, which handheld device is communicating with the transmitter circuit, which transmitter circuit comprises calibrations data representing the actual placement of the transducers in relation to the actual duct, which calibration data is communicated by every connection to the receiver circuit placed in the handheld device.

[0006] Hereby can be achieved that transducers can be permanently placed in ventilation ducts in buildings, where later placement of ultrasound transducers for measurement and for calibration of measurement of an air stream is nearly impossible. But realizing that the price of the transducers is relative low compared to the price of measuring electronics, it is by the pending application possible that the relative cheap transducers are permanently mounted maybe where there is nearly no possibility to have access, and when it is necessary the transducers can be activated by connection to the handheld device. In that way it is possible to measure changes in the air stream, maybe because of pollution of dust or other contamination in air ducts, it is possible by time intervals to control the flow of air and cleaning of air ducts be performed dependent of measured values. It is rather important in larger buildings where air condition is a very important part of the comfort in buildings where thousands of inlets for fresh air can be places in different offices, it is very important a control of the air flow in different parts of a building can be performed not constantly, but after some time intervals for example a few times a year. Placing ultrasound flow measuring systems thousands of places in a building will result in an enormously high cost. But in that situation of course it will be possible continuously to measure the air flow in the building. This continued measurement is of no value because the changes in air flow because of pollution in the ducts take place over longer periods. Therefore, it has a high value that relative cheap transducers are permanently placed everywhere it is necessary to measure the air stream, for example in relation to every air outlet in a building.

[0007] In order to measure the air flow by means of at least a pair of transducers the handheld electronic unit must know a calibration factor depending on the size of the duct and the distance between transducers. The calibration factor may be stored locally together with the transducers and transferred to the electronic unit by some means.

[0008] It is also possible to store other data for example the initial signal levels, the temperature calibration value, set points or other data convenient to have at hand when performing maintenance on the ventilation system.

[0009] Measured data and calibration information can be transmitted from the storing circuit to the receiver circuit by wireless transmission means. It is possible by wireless communication to reach the necessary information from the storing circuit commonly placed in the building where the transmitted information could be for example the actual calibration value for the actual placement of the ultrasound flow measuring device and the actual signals that are received at the transducers. In that way all the electronic handling that is necessary for measuring the time difference in the ultrasound up- and downstream in the air duct can be performed in the handheld device.

[0010] At least calibration data can be communicated by RFID technology. It is possible that the calibration data are transmitted in its own way be the RFID technology. In that way near field communication is possible. If passive RFID technology is in use then the handheld device probably should be as close as a few centimeters from the RFID, in other situations where active RFID technology is used, probably also the measuring data could be transmitted by that technology, but in that situation, the RFID must have a data input and a power supply for the RFID is necessary.

[0011] At least calibration data can be transmitted by a magnetic resonance circuit. It is possible to perform connection of a handheld device by magnetic measurements. A high frequency of magnetic signals can be modulated with data so a relative large data amount can be transmitted by the magnetic resonance technology. Again a near field communication is achieved and the distance between the handheld device and the transmitter circuit has to be reduced to a few centimeters.

[0012] Calibration data can be stored as a bar code at the transmitter circuit, which bar code dataset represent directly or indirectly the calibration data, which calibration data is read by the hand held device by transmission of data representing the actual flow in the duct. It is possible by first installation of the ultrasound flow measuring device to print the calibration data or a reference to the calibration data on a bar code. This bar code can then be placed everywhere there is a surface that can be used near the transmitter circuit. Hereby can the handheld device by a traditional bar code scanner read the calibration information related to the actual ultrasound flow measuring device.

[0013] The transmitter circuit can be connected to a first part of a connector, which handheld device comprises a second part of the connector, which connector transmits at least the calibration data. By using a connector for getting access from the handheld device to the transmitter circuit, it is possible that the storing circuit is designed without any power supply when it is not in use. Therefore, the connector can in some situations start a power and at first then read the calibration data and hereafter start performing measurement.

[0014] The transmitter circuit can comprise at least one EEPROM, which EEPROM comprises at least a data segment representing the calibration data, which calibration data is transmitted from the EEPROM by the connector to the handheld device. It is possible in both wireless connection and by use of a connector to have the calibration data stored in an EEPROM. This EEPROM stores the calibration data highly effective and the data can be read in the EEPROM by most available processors in a serial way reducing the number of pins in the connector. It also possible that the EEPROM is connected to a small processor, which processor then communicate either wireless or through the connector with the handheld device.

[0015] The transmitter circuit comprises at least one DIL switch, which DIL switch comprises at least a data segment representing the calibration data, which calibration data is transmitted from the DIL switch by the connector to the handheld device. By activating or deactivating a number of switches placed on for example a printed circuit board, it is possible in that way to store the data representing the calibration data. The calibration data can be stored directly or indirectly. Indirectly can only data representing the actual flow measuring device be stored in the combination of active or passive DIL switches. In that situation the actual calibration standard is placed in a data storage in the handheld device or in a data base reachable by the handheld device.

[0016] The transmitter circuit can comprise a resistor, which resistor can have a resister value that represents the calibration data for the actual duct, which resister value is transmitted to the handheld device. One of the cheapest electronic components that can be used is a resistor. The resistor value can represent the calibration data. In that way only a measurement of the ohmic value has to be performed in the handheld device for finding the calibration data. In the size of resistors it should be possible to use values from maybe 10 ohms up to several mega ohms where these values can be measured highly effective and the way the value is stored is high reliable.

[0017] The resistance representing the calibration data can be stored in a potentiometer such as a rheostat. It is possible to adjust any potentiometer to a specific value and then simply let that potentiometer remain in that position. In that way it is possible to achieve the resistance that represents the actual calibration data.

[0018] The resistance representing the calibration data can be represented in a plurality of resistors, which resistors are activated by connecting one or more resistors for representing the calibration data. It is possible for example on a printed board just to place a number of resistors to achieve a value that represents the calibration data. It should be possible during production to produce small printed boards with different ohmic values so these relative small printed boards could be placed for example in a connector and then indicating the calibration standard.

[0019] The resistance can be generated at a printed board, at which printed board a number of selected resistors are serial connected, which resistors are short circuited by a conductor at the printed board, which conductor passes a pad, which pad is to be removed for activating the resistor. Placing a row of resistors serial the existing resisting value will be the sum of the resistors. Short cutting all resistors by pads that could be broken away can in that way activate each of the resistors which then are serial connected. In this way can be achieved that a great number of different calibration values can be activated simply by breaking away some pads from a small printed board. In real life it is the different calibration data, maybe limited to a number of different sizes of air ducts. Because air ducts probably only are produced in some standard sizes, only a small number of calibration data are necessary.

[0020] In an alternative embodiment can the calibration data be received by measument of the transmission delay. Because the flow duct has standard sizes and selection of the correct size is possible by the transmission delay.

Description of the Drawing

[0021] 

Fig. 1

shows a first possible embodiment for the invention where the system is in full operation.

Fig. 2

shows the same system but when the system is in a non-operational mode.

Fig. 3

shows one possible embodiment for a connector.

Fig. 4

shows a possible embodiment for a resistor network.

Fig. 5

shows a more detailed disclosure of a resistor network as disclosed at fig. 4.

Detailed Description of the Invention

[0022] Fig. 1 shows one first possible embodiment for the invention for a system 2. Most of the system is placed above a ceiling 3 where an air duct 4 and 5 is indicated. Ultrasound transducers 6,8 are generating a beam of ultrasound across the duct 4. The signals from the ultrasound transducers 6,8 are sent by wires to a first part of a connector 20, which connector has a further part 22, which connects the transducer circuit 6,8 to the handheld device 16. At the handheld device 16 is indicated 123 cubic metres per hour which is an example of a measured value.

[0023] It is therefore possible to perform an effective measurement of the air streaming to the duct in a situation where there is no access directly to the transducers 6,8 because they are placed above the ceiling. All necessary information is by wiring sent to the connector 20, which connects to the other part 22. Therefore, the signals from the transducers 6,8 can be transmitted into the handheld device 16. The handheld device 16 comprises all the necessary electronics for measuring the time difference there is for the ultrasound beam 10 in a first direction following the flow and in a second direction against the flow of air. Based on the difference in the measured time it is possible if the system has the knowledge of the size of the duct 4 to calculate the airflow as indicated at the handheld device 16. In order to achieve a reliable result, it is necessary to perform a calibration of the handheld device 16 according to the size of the duct 4. It is therefore important that calibration data is available for the handheld device in order to achieve reliable measurement.

[0024] Fig. 2 shows the same embodiment as indicated at fig. 1, but at fig. 2 the connector 20 is disconnected and placed inside the transducer circuit 6,8, which has a housing where there is room for the connector 20. In this situation there can be no measurement and the whole system can be switched off because there is no need to have any ultrasound across the duct, because no measurement is performed. The handheld device 16 is also shut off because there is no connection to the connector 22. Hereby is achieved a highly energy effective system, because there is no power consumption in the system when the connector is not in the connected situation.

[0025] Fig. 3 shows a connector 20 and indicates that two high frequency signal lines 34,36 are part of the signal that is transmitted to the connector 20. Further is indicated a resistor 24 and all the lines 34, 36 and resistor 24 are connected through connector legs 38.

[0026] In this way can high frequency signals from the two transducers be directly connected to the handheld device to the legs 38. The resistor 24 can represent the calibration value for the actual device 2. Hereby can the handheld device be calibrated to the actual duct as soon as the high frequency cables are connected to the connector.

[0027] Fig. 4 shows a possible embodiment for the resistor 24. A plurality of resistors is placed on the same printed board forming a serial connection. All resistors indicated at fig. 4 26a-n are short circuited by a printed wire 30 that is running in pads 32, which are part of the printed circuit board 28. The pads 30 are all weakened in their connection because there is one or more holes drilled between the connecting wires 30. Two connectors 38 are indicated which could be part of the connector 20 indicated at fig. 3. In operation will the printed board 28 as seen at fig. 4 have a very low resistance because all the resistors are short circuited so the resistance that could be measured is depending on the resistance of the printed circuit board wires. But in use one or more of the pads 30 are to be broken away in order to achieve the resistance value that represents the actual duct.

[0028] Fig. 5 shows a diagram indicating a plurality of resistors 26 a-n placed on a printed circuit board 28. It can be seen at fig. 5 that the resistors have different ohmic values. Further is indicated that all the resistors are short circuited by printed wires. The short circuit can be broken away for each of the resistors. Their programming of the printed circuit board 28 can be made in a way where starting with the biggest resistor, which is less than the wanted value is broken away. Then further pads 30 are broken away by adjusting closer and closer to the actual value that you want and every possible value that is used for the calibration is possible by the combination of resistant values indicated at fig. 5. Imagine that you want to reach a resistance at a value at 3.230 ohms. Then you can start breaking away the pad that activates one of the 3.000 ohm values. After that you can break away the 200 ohms pad ending up with breaking away one of the small pads for 30 ohms. Many of the values are possible to achieve. When the correct resistance is achieved by breaking away the pads, the printed circuit board 28 can be placed in the connector 20 and an indication of the calibration standard for the actual duct is achieved in a very effective and very cheap way.

Claims

1. System (2) for measuring flow of air in building ventilation flow ducts, which system comprises at least one ventilation flow duct (4), which ventilation flow duct (4) comprises at least two transducers (6,8), which transducers (6,8) generate at least one beam (10) of ultrasound in the ventilation flow duct (4), which transducers (6,8) are connected to a transmitter circuit (20) and to a receiver circuit (22), wherein the air flow is measured by said at least two transducers and calibrated using calibrations data representing the actual placement of the transducers (6,8) in relation to the actual ventilation flow duct (4), the transducers (6,8) are mounted and fixed in relation to the ventilation flow duct (4), which transmitter circuit (20) is permanently connected to the transducers (6,8),
characterized in that said system (2) further comprises a handheld device (16),
wherein
receiver circuit (22) is placed in the handheld device (16), which handheld device (16) is communicating with the transmitter circuit (20), wherein the transmitter circuit (20) communicates said measured data and said calibrations data by every connection to the receiver circuit (22) placed in the handheld device (16).

2. System (2) according to claim 1, characterized in that transmission of measured data and calibration information is transmitted from the transmitter circuit to the receiver circuit by wireless transmission means.

3. System (2) according to claim 2, characterized in that at least calibration data is communicated by RFID technology.

4. System (2) according to claim 2, characterized in that at least calibration data is transmitted by a magnetic resonance circuit.

5. System (2) according to claim 2, characterized in that calibration data are stored as a bar code at the transmitter circuit, which bar code dataset represent directly or indirectly the calibration data, which calibration data is read by the hand held device (16) by transmission of data representing the actual flow in the duct (4).

6. System (2) according to claim 1, characterized in that the transmitter circuit (20) is a first part of a connector (20), which handheld device (16) comprises a second part of the connector (22), which connector (20,22) transmit at least the calibration data.

7. System (2) according to claim 1 or 6, characterized in that the transmitter circuit comprises at least one EEPROM, which EEPROM comprises at least a data segment representing the calibration data, which calibration data is transmitted from the EEPROM by the connector (20, 22) to the handheld device (16).

8. System (2) according to claim 1 or 6, characterized in that the transmitter circuit comprises at least one DIL switch, which DIL switch comprises at least a data segment representing the calibration data, which calibration data is transmitted from the DIL switch by the connector to the handheld device.

9. System (2) according to claim 1 or 6, characterized in that the transmitter circuit comprises a resistor, which resistor has a resistor value that represents the calibration data (18) for the actual ventilation flow duct (4), which resistor value is transmitted to the handheld device (16).

10. System (2) according to claim 9, characterized in that the resistance representing the calibration data is stored in a potentiometer such as a rheostat.

11. System (2) according to claim 9, characterized in that the resistance representing the calibration data is represented in a plurality of resistors, which resistors are activated by connecting one or more resistors for representing the calibration data.

12. System (2) according to claim 11, characterized in that the resistance is generated at a printed board, at which printed board a number of selected resistors are serial connected, which resistors are short circuited by a conductor at the printed board, which conductor passes a pad, which pad is to be removed for activating the resistor.

13. System (2) according to any preceding claim, characterized in that the ultrasound transducers (6, 8) generate a beam of ultrasound across the ventilation flow duct (4).

14. System (2) according to any preceding claim, comprising a ceiling (3) and a ventilation flow duct (4) mounted above the ceiling.

Ansprüche

1. System (2) zur Messung einer Luftströmung in Lüftungs-Strömungskanälen von Gebäuden, welches System mindestens einen Lüftungs-Strömungskanal (4) umfasst, welcher Lüftungs-Strömungskanal (4) mindestens zwei Wandler (6,8) umfasst, welche Wandler (6,8) mindestens einen Ultraschallstrahl (10) in dem Lüftungs-Strömungskanal (4) erzeugen, welche Wandler (6,8) mit einer Senderschaltung (20) und mit einer Empfängerschaltung (22) verbunden sind, wobei die Luftströmung von den mindestens zwei Wandlern gemessen und durch die Verwendung von Kalibrierungsdaten kalibriert wird, welche die tatsächliche Platzierung der Wandler (6,8) in Bezug zum tatsächlichen Lüftungs-Strömungskanal (4) darstellen, wobei die Wandler (6,8) in Bezug zu dem Lüftungs-Strömungskanal (4) montiert und fixiert sind, welche Senderschaltung (20) permanent mit den Wandlern (6,8) verbunden ist, dadurch gekennzeichnet, dass das System (2) ferner eine handgehaltene Vorrichtung (16) umfasst, wobei die Empfängerschaltung (22) in einer handgehaltenen Vorrichtung (16) angeordnet ist, welche handgehaltene Vorrichtung (16) mit der Senderschaltung (20) in Kommunikation steht, wobei die Senderschaltung (20) die gemessenen Daten und die Kalibrierungsdaten durch jede Verbindung mit der in der handgehaltenen Vorrichtung (16) angeordneten Empfängerschaltung (22) übermittelt.

2. System (2) nach Anspruch 1, dadurch gekennzeichnet, dass die Übertragung von gemessenen Daten und Kalibrierungsinformationen von der Senderschaltung zur Empfängerschaltung durch drahtlose Übertragungsmittel übersendet wird.

3. System (2) nach Anspruch 2, dadurch gekennzeichnet, dass mindestens Kalibrierungsdaten durch RFID-Technologie übermittelt werden.

4. System (2) nach Anspruch 2, dadurch gekennzeichnet, dass mindestens Kalibrierungsdaten durch eine magnetische Resonanzschaltung übertragen werden.

5. System (2) nach Anspruch 2, dadurch gekennzeichnet, dass Kalibrierungsdaten als ein Barcode in der Senderschaltung gespeichert sind, welcher Barcode-Datensatz direkt oder indirekt die Kalibrierungsdaten darstellt, welche Kalibrierungsdaten von der handgehaltenen Vorrichtung (16) durch die Übertragung von die tatsächliche Strömung im Kanal (4) darstellenden Daten gelesen werden.

6. System (2) nach Anspruch 1, dadurch gekennzeichnet, dass die Senderschaltung (20) ein erster Teil eines Verbinders (20) ist, welche handgehaltene Vorrichtung (16) einen zweiten Teil des Verbinders (22) umfasst, welcher Verbinder (20,22) mindestens die Kalibrierungsdaten überträgt.

7. System (2) nach Anspruch 1 oder 6, dadurch gekennzeichnet, dass die Senderschaltung mindestens einen EEPROM umfasst, welcher EEPROM mindestens ein die Kalibrierungsdaten darstellendes Datensegment umfasst, welche Kalibrierungsdaten vom EEPROM durch den Verbinder (20, 22) an die handgehaltene Vorrichtung (16) übertragen werden.

8. System (2) nach Anspruch 1 oder 6, dadurch gekennzeichnet, dass die Senderschaltung mindestens einen DIL-Schalter umfasst, welcher DIL-Schalter mindestens ein die Kalibrierungsdaten darstellendes Datensegment umfasst, welche Kalibrierungsdaten vom DIL-Schalter durch den Verbinder an die handgehaltene Vorrichtung übertragen werden.

9. System (2) nach Anspruch 1 oder 6, dadurch gekennzeichnet, dass die Senderschaltung einen Widerstandskörper umfasst, welcher Widerstandskörper einen Widerstandskörperwert aufweist, der die Kalibrierungsdaten (18) für den tatsächlichen Lüftungs-Strömungskanal (4) darstellt, welcher Widerstandskörperwert an die handgehaltene Vorrichtung (16) übertragen wird.

10. System (2) nach Anspruch 9, dadurch gekennzeichnet, dass der die Kalibrierungsdaten darstellende Widerstand in einem Potentiometer wie etwa einem Rheostat gespeichert ist.

11. System (2) nach Anspruch 9, dadurch gekennzeichnet, dass der die Kalibrierungsdaten darstellende Widerstand in einer Vielzahl von Widerstandskörpern dargestellt ist, welche Widerstandskörper durch das Verbinden eines oder mehrerer Widerstandskörper aktiviert werden, um die Kalibrierungsdaten darzustellen.

12. System (2) nach Anspruch 11, dadurch gekennzeichnet, dass der Widerstand an einer Leiterplatine erzeugt wird, an welcher Leiterplatine eine Anzahl von ausgewählten Widerstandskörpern in Reihe geschaltet ist, welche Widerstandskörper durch einen Leiter an der Leiterplatine kurzgeschlossen sind, welcher Leiter ein Pad passiert, welches Pad zur Aktivierung des Widerstandskörpers zu entfernen ist.

13. System (2) nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die Ultraschallwandler (6, 8) einen Ultraschallstrahl über den Lüftungs-Strömungskanal (4) erzeugen.

14. System (2) nach einem der vorhergehenden Ansprüche, das eine Decke (3) und einen über der Decke montierten Lüftungs-Strömungskanal (4) umfasst.

Revendications

1. Système (2) pour mesurer le débit d'air dans des conduits d'écoulement à ventilation des bâtiments, lequel système comprend au moins un conduit d'écoulement à ventilation (4), ledit conduit d'écoulement à ventilation (4) comprenant au moins deux transducteurs (6,8), lesdits transducteurs (6,8) générant au moins un faisceau (10) d'ultrasons dans le conduit d'écoulement à ventilation (4), lesdits transducteurs (6,8) étant connectés à un circuit émetteur (20) et à un circuit récepteur (22), dans lequel le débit d'air est mesuré par lesdits au moins deux transducteurs et étalonné en utilisant des données d'étalonnage représentant le positionnement réel des transducteurs (6,8) par rapport au conduit d'écoulement à ventilation réel (4), les transducteurs (6,8) étant montés et fixés par rapport au conduit d'écoulement à ventilation (4), ledit circuit émetteur (20) étant connecté en permanence aux transducteurs (6,8), caractérisé en ce que ledit système (2) comprend en outre un dispositif portatif (16), ledit circuit récepteur (22) étant placé dans le dispositif portatif (16), ledit dispositif portatif (16) étant en communication avec le circuit émetteur (20), ledit circuit émetteur (20) communiquant lesdites données mesurées et lesdites données d'étalonnage par chaque connexion au circuit récepteur (22) placé dans le dispositif portatif (16).

2. Système (2) selon la revendication 1, caractérisé en ce que la transmission des données mesurées et des informations d'étalonnage est transmise du circuit émetteur au circuit récepteur par des moyens de transmission sans fil.

3. Système (2) selon la revendication 2, caractérisé en ce qu'au moins les données d'étalonnage sont communiquées par la technologie RFID.

4. Système (2) selon la revendication 2, caractérisé en ce qu'au moins les données d'étalonnage sont transmises par un circuit à résonance magnétique.

5. Système (2) selon la revendication 2, caractérisé en ce que les données d'étalonnage sont stockées sous forme de code à barres dans le circuit émetteur, ledit ensemble de données de codes à barres représentant directement ou indirectement les données d'étalonnage, lesdites données d'étalonnage étant lues par le dispositif portatif (16) par transmission de données représentant un écoulement réel dans le conduit (4).

6. Système (2) selon la revendication 1, caractérisé en ce que le circuit émetteur (20) est une première partie d'un connecteur (20), ledit dispositif portatif (16) comprenant une deuxième partie du connecteur (22), ledit connecteur (20,22) transmettant au moins les données d'étalonnage.

7. Système (2) selon la revendication 1 ou 6, caractérisé en ce que le circuit émetteur comprend au moins une EEPROM, ladite EEPROM comprenant au moins un segment de données représentant les données d'étalonnage, lesdites données d'étalonnage étant transmises à partir de l'EEPROM par le connecteur (20, 22) sur le dispositif portatif (16).

8. Système (2) selon la revendication 1 ou 6, caractérisé en ce que le circuit émetteur comprend au moins un commutateur DIL, ledit commutateur DIL comprenant au moins un segment de données représentant les données d'étalonnage, lesdites données d'étalonnage étant transmises à partir du commutateur DIL par le connecteur sur le dispositif portatif.

9. Système (2) selon la revendication 1 ou 6, caractérisé en ce que le circuit émetteur comprend une résistance, ladite résistance ayant une valeur de résistance qui représente les données d'étalonnage (18) du conduit d'écoulement à ventilation (4) réel, ladite valeur de résistance étant transmise au dispositif portatif (16).

10. Système (2) selon la revendication 9, caractérisé en ce que la résistance représentant les données d'étalonnage est stockée dans un potentiomètre tel qu'un rhéostat.

11. Système (2) selon la revendication 9, caractérisé en ce que la résistance représentant les données d'étalonnage est représentée dans une pluralité de résistances, ces résistances étant activées en connectant une ou plusieurs résistances pour représenter les données d'étalonnage.

12. Système (2) selon la revendication 11, caractérisé en ce que la résistance est générée au niveau d'une carte imprimée sur laquelle sont connectées en série un certain nombre de résistances sélectionnées, résistances qui sont court-circuitées par un conducteur situé sur la carte imprimée, ledit conducteur passant un patin, ledit patin devant être retiré pour activer la résistance.

13. Système (2) selon l'une quelconque des revendications précédentes, caractérisé en ce que les transducteurs d'ultrasons (6, 8) font générer au moins un faisceau d'ultrasons à travers le conduit d'écoulement à ventilation (4).

14. Système (2) selon l'une quelconque des revendications précédentes, comprenant un plafond (3) et un conduit d'écoulement à ventilation (4) monté au-dessus du plafond.

Drawing